Short-circuiting device for electric motors.



C. L. KENNEDY. SHORT CIRCUITING DEVICE FOR ELECTRIC MOTORS.

APPLICATION FILED AUGJ, 1914.

Patented July 6, 1915.

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CARLTON L. KENNEDY, OF SOUTH BRAINTREE, MASSACHUSETTS, ASSIiSrNOR TO THE HOLTZER-CABOT 'ELECTBIC COMPANY. OF BROOKLINE, MASSACHUSETTS, A. COR- POBATION or mssacnusnrrs.

To all whom it may concern:

Be it known that I, CARLTON L. KENNEDY,

a citizen of the United States, residing at South Braintree,in the county of Norfolk and State of Massachusetts, have invented certain new and useful Improvements inShort-Circuiting Devices for Electric Motors; and

' I do hereby declare the following to be a' full,

clear, and exact description of the invention, such aswill enable others skilled in the art 'to which it appertains to make and use the and the motor thereafter This invention relates to improvements in short-clrcuitlng devlces for electric motors and more particularly to inductlon motors.

. In order that this type of motor may be selfstarting it is commonly provided, in addition to a primary or stator winding directly connected with the source of eurrent,'witha commutator connectedby windings with the rotor, similar to av direct current motor. The commutato'r as'thus connected is used .tostart the motor and bring it up to the required speed at which point the commutator with the rotor winding is short-circuited,

operates as an induction motor. Y

The devices most commonly employed for efiectuating the short-circuiting operate auholds the contacting members against the commutator is exerted directly by two means, namely, the spring and the centrifugal force. The travel of the contacting members upon thecommutator under these conditions tends to score channels in the soft metal of the commutator. This scoring is detrimental to the eflicient and continued service of the motor.

One object of the present invention is to produce a short-circuiting device of such Specification of Letters Patent.

sno'mr-cmcuxtrme DEVICE FOR ELECTRIC MOTORS.

Patented uly 6, 1915.

I Application a... August 1,1914. Serial No. 354,522.

construction that the centrifugally-operated members will not score the commutator. Thls is effected by constructing the device of two parts hinged together, the one part acted upon by the spring and the other part bemg directlysubjected to centrifugal action only. a

Other objects of the invention will hereinafter appear. In the accompanying drawings illustratmg the preferred form of the invention: Figure 1 is an end elevation of a commutator with the improved short-eircuiting de-" vices applied thereto; Fig. 2 is a sectional new on line 44 of Fig. 1, showing the contact blocks 1n contact with the commutator;

and Fig. 3 is a similar view showing the contact blocks out of contact with the commutator.

The commutator segments 5 are mounted upon a commutator spool 6 which is rigidly secured to the rotor shaft 7 by'means of the set screw 8. The outer end of the spool has an upwardly projecting flange or lip 9 having a beveled inner face. The inner end of the periphery of the spool is threaded to receive thereon an annular nut 10 having a beveled face corresponding to the inner face of the lip 9. The commutator segments are firmly positioned between the lip and the nut, being insulated from them in the usual manner. Between the commutator spool and the rotor shaft is formed a rockerarm chamber 11 and within this chamber is situated an annular sleeve 12 loosely slidable upon the rotor shaft 7 and provided with radial slots which are adapted to receive and loosely hold the rocker-arms 13. The rocker-arms are somewhat triangular in shape and are each furnished with a heel 15 depending from the base end. This heel receives the thrust of the spring 16 interposed between the outer end of the annular sleeve 12 and the adjustable ring 17 by which the tension of the spring may be regulated, the ring being secured to the shaft by the set screw 18. In order that the rocking action of the heel 15 may not wear away the inner end of the sleeve 12 a hardened steel washer 19 is provided. The pressure of the spring tends constantly to force the base 20 of the rocker-arms. against. the end wall of the chamber, thereby keeping the bottomside 21 its of the arms contiguous to the bottoms of the slots in the annular sleeve 12, as shown in Fig. 2. g

On the outer end of each rocker-arm is pivoted a substantially U-shaped contact 'block 22.

lies one of the features of my invention, that It will "be observed, and herein the; center of; gravity of the contact block hes beyond the pivots 23, that is to say, be-

yond the plane of the pivots. The free or contacting end 2ft of the contactblock projects inwardly'toward thecommutator from the center of gravity of the blocks, in consequence thereof, when, the blocks are caused to fiy outwardly under centrifugal force,

they must come in contact, first with the outer end of the commutator spool, then with the outer end of the commutator itself. The stronger the action of the centrifugal force the greater will be the pressure of the block against the commutator. 'It will be further and moreparticularly observed that no part of the pressure of the spring 16 is exerted upon the contact blocks. The pressure of the spring is entirely taken up by the rocker-arms.

It 's well known that a repulsion motor willfoperate as an induction motor with the commutator short circuited at a number of points,, the efiiciency and maximum load increasingffirst very rapldly as the number of short circuiting points is increased above two, butjincreasing very slowly after five or six points on the commutator have been connected; Furthermore, a device of this sort is usually used with a so-called wave or'two-cii'cuit winding on the armature, and

asthese motors are usually wound to have 4, 6 or" 8, poles, it is evident that in order to obtain as many electrically effective contact points on the commutator as there are contact blocks, it is desirable to employ a number of contact blocks which will not be divisible by the number of" pairs of poles on the motor. In the illustrated embodiment of theinvention, eleven contact blocks are used, .as this has beenfou'nd to give good results.

In use my improved short-circuiting device o erates asfollowsl: Immediate u on P y P starting up the motor the contact blocks 22 under the action of centrifugal .force are thrown against the outer end of the commutatorisp'ool, as shown in Fig. 3. As the speed of the motor increases, the ends of the contact blockstravel across the face of the spool until-they reach the commutator, as shown in Fig. 2, when the motor attains the predetermined critical speed. The outward throw of theblocks is limited by the rocker arms which, beingpulled outward radially are brought up against the sidewall 25 .of the rocker-arm chamber. "By' ,properly ad.-

. justing the strength and tension of the spring 16 to the weight of the contact blocks,

the centrifugal force due to the outward travel of the blocks may be made to increase faster than the increase in the tension of the spring, with the result that the contact block will attain a short-circuiting contact with thecommutator by a quick movement.

I have described the preferred form of my invention; it is obvious, however, that it may be embodied in other forms. It is my purpose to claim these constructions broadly within the spirit of thefollowin claims. I 1. A short circuiting device for electric motors, having, in combination, a commutator, and a plurality of rocker-arms pro-,

vided with'means ivoted at theirouter ends adapted when sub ected to centrifugal force to be brought into contact with the commug tator.

2. A short circuiting device for electric motors, having, in combination, a commu tator, of a plurality of rocker-arms, and a plurality of contact blocks pivoted at the outer ends of the rocker-arms and adapted under the influence of centrifugal force to contact the commutator.

3. A short circuiting device for electric motors, having, in combination, a commutator, an annular sleeve provided with radial slots, a plurality of rocker-arms mov-' able in said slots, and a plurality of U- shaped contact blocks pivoted at the outer ends of the rocker-arms, and adapted to contact the commutator at a predetermined motor speed, the center of gravity of the contact blocks lying beyond the pivots.

4. A short circuiting device for electric motors, having, in combination, a commutator, a plurality of rocker-arms, an annulai sleeve supporting the rocker-arms, and

contact blocks pivoted respectively on the rocker-arms, the center of gravity of the contact blocks being beyond the pivots and the free ends of the contact blocks being interposed between their centers of gravity and the commutator, so that when the contact blocks are acted upon by centrifugalforce their free ends are brought into con-- tact with the commutator.

5. A short circuiting device motors, having, in combination, a shaft, :1.

for electric nuence of centrifugal force at a predeter' mined speed to overcome the action of the spring u on .the rocker-arms and force them against the side wall of the chamber.

6. A short-circuiting device for electric motors, having, in combination, a commutator, an armature shaft, an annular sleeve slidable on the armature shaft and provided with radial slots, rocker-arms movable in the slots, a collar engaging a projection from said arms, a spring actin upon the collar and normally holding the ottom side of the rocker-arms against the bottom of the slots of said sleeve, and contact blocks pivotally connected to one end of said rocker-arms respectively and adapted at a predetermined speed to fly outwardly, thereby overcoming the tension of the spring and causing the rocker-arms to move radially outward in said slots.

7. A short circuiting device for electric motors, having in combination, a commutator, and a short 'circuiting device therefor consisting of spring resisted rocker-arms each provided with a pivoted centrifugal contact block.

8. A short circuiting device for electric motors, having, in combination, a commutator, rocker-arms and contact blocks pivoted on the rocker arms constructed and arranged so that they may be brought into contact with the commutator by centrifugal force, the pivots being adapted to move in the line of the centrifugal force.

, 9. A short circuiting device for electric motors, having, in combination, a commutator, two articulated short circuiting members and resilient means for normally holding the short circuiting members in inoperative position, said members being constructed and arranged to be brought into operative position'by centrifugal force, one of said members being adapted to compress the resilient means to permit the other member to contact the commutator with a pressure equal to the effect of the centrifugal force on said member.

10. A short circuiting device for electric motors, having, in combination, a short-circuiting contact device, a commutator having a surface over which the contact device is movable outwardly to operative position, a spring for returning the contact device to inoperative position. and connections between the cont act device and the spring subject to centrifugal force whereby the contact device may be moved outwardly as aforesaid, saidcg connections being constructed and arranged to resolve the centrifugal force to a comparatively great component effective against the spring and a comparatively small component effective to press the contact device against said surface.

CARLTON L. KENNEDY. \Vitnesses:

Gno. E. Srnnmxs, ALICE AcKnoro. 

